Views: 0 Author: Nancy Liu Publish Time: 2026-08-03 Origin: Zhenghao Machinery
Table of Contents
When machinists talk about vise selection, the conversation almost always focuses on the vise body: jaw width, clamping force, body height, precision standard. The jaw type — the actual interface between the vise and the workpiece — receives far less attention.
This is a mistake.
The jaw type determines how the clamping force is distributed across the workpiece surface. It determines whether the workpiece moves under cutting load. It determines whether the workpiece is marked, scratched, or deformed by the clamping action. And it determines how much of the workpiece is accessible to the cutting tool.
Choosing the wrong jaw type for a given operation does not just reduce efficiency — it can cause scrap, surface damage, and positional errors that no amount of precision in the vise body can correct.
This guide covers every major CNC vise jaw type available for the GT Series Precision Modular Vise, explains the engineering logic behind each design, and provides a clear selection framework based on workpiece material, geometry, and operation type.
A vise body provides clamping force. The jaw converts that clamping force into a holding action on the workpiece. The conversion is not perfect — it depends on the jaw geometry, the jaw material, and the workpiece surface condition.
Consider two scenarios with identical vise bodies and identical clamping force:
Scenario A: Flat hardened steel jaws on a ground steel workpiece. The jaw face contacts the workpiece across its full width. The clamping force is distributed evenly. The workpiece is held securely with minimal surface marking.
Scenario B: Flat hardened steel jaws on a round bar. The jaw face contacts the workpiece at a single line (the tangent point). The clamping force is concentrated at that line. The workpiece is held insecurely — it can rotate under cutting load — and the jaw face marks the workpiece surface at the contact line.
Same vise body. Same clamping force. Completely different holding performance. The difference is the jaw-to-workpiece interface geometry — which is entirely determined by the jaw type.
The GT Series interchangeable jaw system is designed around this principle. Rather than accepting a single jaw type as a compromise for all applications, the GT Series provides a range of jaw types that can be matched precisely to the workpiece geometry and operation — and swapped between jobs without removing the vise body from the machine table.
Flat jaws are the default jaw type supplied with most precision modular vises. The jaw face is a flat, precision-ground hardened steel surface that contacts the workpiece across its full width.
The flat jaw face contacts the workpiece on its flat side faces. The clamping force is distributed across the full contact area. For workpieces with flat, parallel side faces — the most common workpiece geometry in prismatic machining — flat jaws provide the most consistent and repeatable clamping.
GT Series flat jaws are manufactured from 20CrMnTi alloy steel, carburized and hardened to HRC 58–62. This hardness level is critical: jaws that are softer than the workpiece material will deform under repeated clamping, causing the jaw face to become non-flat and introducing positional errors over time.
Condition | Flat jaw suitability |
Workpiece has flat, parallel side faces | ✓✓✓ Ideal |
Workpiece is a prismatic block or plate | ✓✓✓ Ideal |
Precision grinding operation | ✓✓✓ Ideal — consistent Z-height seating |
CNC milling, Op1 on a raw block | ✓✓ Very good |
Workpiece is round bar or cylinder | ✗ Poor — use V-groove jaws |
Workpiece has a complex profile | ✗ Poor — use soft jaws |
Workpiece is aluminium or soft material | ✓ Acceptable — but may mark surface |
Flat jaws will mark soft workpiece surfaces (aluminium, copper, plastic) under high clamping force. For soft materials, consider soft jaws or jaw face inserts. For round or irregular workpieces, flat jaws provide inadequate contact area and should not be used.
V-groove jaws incorporate a precision-ground V-shaped channel in the jaw face. The V-groove self-centres round, hexagonal, and other non-flat workpieces, providing two-line contact instead of the single-line contact that flat jaws would provide on a round workpiece.
When a round bar is placed in V-groove jaws, the bar contacts the V at two points on each jaw — four contact points total across both jaws. The V geometry forces the bar to self-centre: as clamping force increases, the bar is driven into the V until it reaches the equilibrium position where the clamping forces from both V faces are equal. This self-centring action is repeatable — the bar returns to the same position on every clamping cycle.
The self-centring also provides a known geometric relationship between the bar's centreline and the vise jaw reference surface. For turning or milling operations where the bar's centreline is the datum, this known relationship allows the work offset to be calculated from the jaw reference rather than probed from the bar surface.
Condition | V-groove jaw suitability |
Round bar stock | ✓✓✓ Ideal |
Hexagonal bar stock | ✓✓✓ Ideal |
Octagonal or multi-flat profiles | ✓✓ Very good |
Turned components (cylindrical workpieces) | ✓✓✓ Ideal |
Pipe and tube clamping | ✓✓ Good — verify wall thickness |
Prismatic block (flat sides) | ✗ Poor — use flat jaws |
The GT Series V-groove jaw range is available for all GT jaw widths from GT100 to GT300. The V-groove angle is standardised across the range, allowing the same work offset calculation method to be used regardless of jaw width. All V-groove jaws are ground to the same 0.005 mm / 100 mm parallelism and squareness standard as the flat jaws.
The V-groove jaw is not suitable for workpieces that have been partially machined on one face — for example, a round bar that has had a flat milled on one side. The flat disrupts the self-centring action. For partially machined workpieces, soft jaws profiled to the workpiece geometry provide more consistent clamping.
Serrated jaws have a knurled or cross-hatched pattern machined into the jaw face. The serrations bite into the workpiece surface under clamping force, providing a mechanical interlock between the jaw and the workpiece.
Under clamping force, the serration peaks penetrate slightly into the workpiece surface. This creates a mechanical interlock that resists both axial (along the jaw face) and lateral (perpendicular to the jaw face) movement of the workpiece under cutting load.
The result is a significantly higher effective holding force than flat jaws at the same clamping torque — because the serrations add mechanical interlock to the friction-based holding mechanism of flat jaws.
Condition | Serrated jaw suitability |
Heavy roughing operations with high cutting forces | ✓✓✓ Ideal |
Hard materials (hardened steel, titanium, Inconel) | ✓✓✓ Ideal |
Large depth of cut, aggressive feed rates | ✓✓✓ Ideal |
Workpiece surface finish is not critical (will be machined away) | ✓✓✓ Ideal |
Finishing operation where surface must be preserved | ✗ Never — serrations mark the surface |
Thin-walled workpieces | ✗ Avoid — serrations concentrate stress |
Soft materials (aluminium, brass, plastic) | ✗ Avoid — serrations cause deep surface damage |
Serrated jaws are for roughing only. The serration marks left on the workpiece surface are permanent. If the clamped face will be visible in the finished part, or if the clamped face is a precision reference surface for a subsequent operation, serrated jaws are not appropriate.
The correct workflow for parts requiring both roughing and finishing:
Op1 (roughing): Serrated jaws — maximum grip, aggressive cutting parameters
Op2 (finishing): Flat jaws or soft jaws — no surface marking, consistent positioning
With the GT Quick-Change Jaw System, this jaw swap takes seconds without disturbing the vise body position.
Step jaws have a stepped profile on the jaw face. The workpiece sits on the lower step of the jaw, with the upper portion of the workpiece extending above the top of the jaw face. This raises the workpiece above the vise body and eliminates the need for parallel blocks.
In a standard flat jaw setup, the workpiece sits on the vise bed with the jaw faces contacting the workpiece sides. The workpiece's bottom face is at vise bed level. If the machining program needs to access the workpiece close to its bottom face, the jaw body obstructs the tool approach.
Step jaws solve this by raising the workpiece. The workpiece sits on the step (which is precision-ground to a known height above the jaw base), with the lower portion of the workpiece elevated above the vise body. The tool can now approach the lower workpiece faces from the side without obstruction.
Many machinists use parallel blocks (precision-ground rectangular blocks placed under the workpiece) to raise the workpiece above the vise bed. Step jaws eliminate the need for parallel blocks entirely:
Parallel blocks | Step jaws |
Must be selected to match workpiece height | Step height is fixed and known |
Risk of falling out during machining | Integral to jaw — cannot fall out |
Add a setup step (selection, placement, verification) | No additional setup step |
Require probing to verify workpiece height | Step height is a known constant |
Can shift under vibration | Precision-ground step — no movement |
For 5-axis machining in particular, step jaws are the preferred solution because they raise the workpiece above the vise body, increasing the angular clearance available for tilted spindle approaches — as discussed in our 5-axis workholding guide.
Condition | Step jaw suitability |
5-axis machining requiring access to lower workpiece faces | ✓✓✓ Ideal |
Operations previously requiring parallel blocks | ✓✓✓ Ideal |
Thin workpieces that need to be raised above the vise body | ✓✓✓ Ideal |
High-volume production where setup time must be minimised | ✓✓ Very good |
Workpiece height varies between jobs | ✗ Use flat jaws + parallel blocks for flexibility |
Thread hole jaws — also called soft jaw carriers or machinable jaw bases — are hardened steel jaw bodies with a grid of threaded holes on the jaw face. These threaded holes accept custom-machined aluminium or steel soft jaw inserts that are bolted to the carrier and then machined to match the exact profile of the workpiece.
The thread hole jaw carrier provides the structural interface between the vise body and the soft jaw insert. The carrier is precision-ground and hardened (HRC 58–62), providing a stable, repeatable mounting surface. The soft jaw insert — typically aluminium for most applications, steel for heavy-duty work — is bolted to the carrier and then machined in situ (while clamped in the vise) to create a pocket that exactly matches the workpiece profile.
Because the soft jaw pocket is machined in the vise that will hold the workpiece, the pocket geometry is perfectly aligned with the vise's reference surfaces. When the workpiece is placed in the pocket, it is automatically positioned to the same datum as the machined pocket — with repeatability limited only by the fit between the workpiece and the pocket, typically 0.005–0.01 mm.
The GT Series thread hole jaw range provides the carrier jaw bodies for all GT jaw widths (GT125 to GT300). The threaded hole grid is standardised across the range, and aluminium soft jaw blanks are available as matching accessories. The carrier jaws are compatible with the GT Quick-Change Jaw System, allowing the entire soft jaw assembly (carrier + soft jaw insert) to be swapped in seconds.
Condition | Soft jaw suitability |
Workpiece has a complex or irregular profile | ✓✓✓ Ideal |
Workpiece surface must not be marked | ✓✓✓ Ideal — aluminium soft jaw is softer than workpiece |
Op2 clamping on a previously machined face | ✓✓✓ Ideal — pocket matches Op1 machined geometry |
High-volume production of a single part number | ✓✓✓ Ideal — soft jaw is a dedicated fixture |
Thin-walled or delicate workpieces | ✓✓✓ Ideal — full-face contact distributes clamping force |
Castings or forgings with irregular surfaces | ✓✓✓ Ideal — pocket conforms to actual surface |
Low-volume or one-off jobs | ✗ Not economical — use flat or step jaws |
Workpiece geometry changes frequently | ✗ Each geometry requires a new soft jaw |
Soft jaw material | Best for | Notes |
Aluminium (6061) | Most CNC milling and finishing operations | Will not mark workpiece; easy to machine; replace when worn |
Mild steel | Heavy roughing on hard materials | More durable than aluminium; may mark soft workpiece surfaces |
Nylon / UHMWPE | Delicate surfaces, optical components, finished parts | Maximum surface protection; limited clamping force capacity |
The theoretical benefit of having multiple jaw types is clear. The practical barrier is the time required to change jaw types between jobs. On a conventional vise, changing jaw type means:
Removing the bolts that secure the current jaws
Removing the current jaws
Installing the new jaws
Torquing the bolts to specification
Verifying the jaw face position with a dial indicator
On a busy shop floor, this process takes 5–15 minutes per vise — long enough that many shops simply leave the same jaw type installed for all jobs, accepting the performance compromise rather than paying the setup time cost.
The GT Precision Modular Vise Quick-Change Jaw System eliminates this barrier. The jaw inserts are secured by a precision-ground dovetail interface and a single locking mechanism. Jaw changes are completed in seconds — no bolts, no torque wrench, no dial indicator verification required. The dovetail interface returns the new jaw to within 0.003–0.005 mm of the previous jaw's position automatically.
The practical result: A shop running the GT Quick-Change system can change jaw types between every job without any meaningful setup time penalty. The jaw type is always matched to the current job's requirements — not to the lowest-common-denominator compromise that fits all jobs acceptably.
Jaw type | Quick-Change compatible | Available sizes |
Flat hard jaws | ✓ | GT150×200, GT150×300 |
V-groove jaws | ✓ | GT150×200, GT150×300 |
Thread hole jaws (soft jaw carrier) | ✓ | GT150×200, GT150×300 |
Step jaws | ✓ | GT150×200, GT150×300 |
Use this matrix to identify the correct jaw type for your application:
Workpiece geometry | Operation type | Workpiece material | Recommended jaw type |
Flat parallel sides | Precision milling / grinding | Any | Flat hard jaws |
Flat parallel sides | Heavy roughing | Steel / titanium | Serrated jaws |
Flat parallel sides | Finishing / no surface marks | Aluminium / soft | Soft jaws |
Round bar / cylinder | Any milling operation | Any | V-groove jaws |
Hexagonal bar | Any milling operation | Any | V-groove jaws |
Thin plate / needs elevation | 5-axis / multi-face access | Any | Step jaws |
Complex profile / irregular | Any | Any | Soft jaws |
Previously machined face (Op2) | Finishing / precision | Any | Soft jaws |
Casting / forging surface | Roughing | Any | Serrated jaws or Soft jaws |
Delicate / finished surface | Light finishing | Any | Soft jaws (aluminium or nylon) |
All GT Series jaw types are compatible with the full range of GT vise bodies. The jaw-to-body interface is standardised across the GT100–GT300 range, ensuring that jaw types purchased for one GT vise body can be used on any other GT vise body of the same jaw width.
GT jaw width | Flat | V-groove | Serrated | Step | Thread hole (soft jaw carrier) |
GT100 (100 mm) | ✓ | ✓ | ✓ | ✓ | ✓ |
GT125 (125 mm) | ✓ | ✓ | ✓ | ✓ | ✓ |
GT150 (150 mm) | ✓ | ✓ | ✓ | ✓ | ✓ |
GT175 (175 mm) | ✓ | ✓ | ✓ | ✓ | ✓ |
GT200 (200 mm) | ✓ | ✓ | ✓ | ✓ | ✓ |
GT300 (300 mm) | ✓ | ✓ | ✓ | ✓ | ✓ |
All jaw types: 20CrMnTi alloy steel · HRC 58–62 · Parallelism 0.005 mm/100 mm · Squareness 0.005 mm/100 mm
Explore the complete jaw range at www.pyzhjx.com/gtprecisionmodularvisejaws.
For a shop running a GT Series vise system, the most efficient approach is to build a jaw library — a set of jaw types held in stock and swapped into the vise as required by each job. With the GT Quick-Change system, this library is immediately accessible at the machine without any setup time penalty.
Jaw type | Quantity | Primary use |
Flat hard jaws | 2 pairs | Default — prismatic workpieces, grinding |
V-groove jaws | 1 pair | Round and hexagonal bar stock |
Step jaws | 1 pair | 5-axis work, thin plates |
Thread hole jaws (carrier) | 1 pair | Soft jaw base for complex profiles |
Aluminium soft jaw blanks | 4–6 pairs | Custom profiles — machine as needed |
Total investment: 5 jaw type configurations covering the full range of typical CNC milling and grinding applications. With the GT Quick-Change system, any of these configurations is accessible in under 30 seconds at the machine.
The vise body provides the clamping force. The jaw type determines how that force is applied to the workpiece. Choosing the jaw type deliberately — based on the workpiece geometry, material, and operation — is one of the highest-leverage decisions in CNC workholding setup.
The GT Series interchangeable jaw system provides every jaw type needed for precision CNC machining:
Flat jaws for prismatic workpieces and precision grinding
V-groove jaws for round and hexagonal stock
Serrated jaws for heavy roughing on hard materials
Step jaws for 5-axis work and thin-plate elevation
Thread hole jaws for soft jaw mounting on complex profiles
Combined with the GT Quick-Change Jaw System, jaw type changes between jobs take seconds — making it practical to always use the optimal jaw type for every operation, rather than accepting a compromise.
Explore the full GT Series jaw range and vise bodies at www.pyzhjx.com/product-6-1.html, or contact the Zhenghao technical team for jaw selection advice on your specific application.
Email: zhjx@pyzhjx.com
Phone / WhatsApp: +86-18660185316
Website: www.pyzhjx.com
Flat hard jaws are the most common jaw type for general CNC milling of prismatic workpieces. They provide consistent, repeatable clamping on flat parallel side faces and are compatible with the full range of workpiece materials. For most shops, flat jaws are the default — and other jaw types are selected when the workpiece geometry or operation requires a different interface.
Not recommended. Serrated jaws are designed to bite into the workpiece surface to create a mechanical interlock. On aluminium, the serrations will create deep marks that may not be removed by subsequent machining if the clamped face is a reference surface. For aluminium, use flat jaws for standard operations or aluminium soft jaws for complex profiles.
Aluminium soft jaw inserts wear gradually with repeated clamping cycles. For high-volume production of a single part number, a set of aluminium soft jaws typically lasts several hundred to several thousand clamping cycles before the pocket geometry degrades enough to affect positioning accuracy. When the repeatability of the soft jaw setup exceeds the part tolerance, the soft jaw blank is re-machined or replaced. Steel soft jaw inserts last significantly longer but are harder to machine.
V-groove jaws can be used on square bar stock, but the self-centring action is less consistent than on round stock because the V contacts the square bar at its corners rather than on its faces. For square bar stock, flat jaws provide more consistent clamping. V-groove jaws are optimised for round, hexagonal, and other rotationally symmetric profiles.
Both step jaws and parallel blocks raise the workpiece above the vise bed. The key differences are: (1) step jaws are integral to the jaw assembly and cannot fall out during machining; (2) the step height is a fixed, known constant that does not need to be measured or verified; (3) step jaws eliminate the setup time required to select, place, and verify parallel blocks; (4) step jaws are compatible with the GT Quick-Change system, allowing the elevation to be changed between jobs in seconds. For high-volume production where the same elevation is used repeatedly, step jaws are significantly more efficient than parallel blocks.
GT Series jaw types are designed for the GT Series vise body interface. They are not guaranteed to be compatible with other brands of modular vises, as the jaw-to-body interface geometry varies between manufacturers. If you are using a non-GT vise body, contact the Zhenghao technical team to discuss compatibility or custom jaw manufacturing options.
